Percussion system for an electronic musical instrument



w. H. KRUG 3,073,204

ELECTRONIC MUSICAL INSTRUMENT Jam. 15, 1963 PERCUSSION SYSTEM FOR AN v//J/zad/ Filed Dec.

vJ0 d d e e@ o u PERCUJS/ON C @27m/veeg@ United States Patent O s 073,204 PEncUssioN sYsriiM non AN nrnornosuc Musicali; Instant/rana William H. Krug, Janesville, Wis., assigner to Gibbsl This invention is concerned with a percussion `system for an electronic musical instrument.

In general a percussive note is characterized by a steep leading edge of relatively high initial amplitude followed by a gradual amplitude decrease. Percuss1on instruments include drums, cymbal, chimes and thelike. In certain electrical musical instruments, as in an electronic organ, it is desirable to provide a percussive eiiect which may be used to simulate various musical devices such as the chimes, carillon and electric guitar, for example, depending upon the selection oftonal qualities of the notes and the rate of amplitude decrease or decay following tone actuation. f 7

A principal object of this'invention is the provision of a novel system for producing percussive effects which is particularly designed for an electronic organ having a photoelectric cell tone generating system.

One feature of the invention is the provision, in an electronic musical instrument utilizing a tone generator incorporating a lamp, of a keying system including a source of potential for energizing the lamp, keying means for connecting the lamp and source to apply a potential to the lamp and means responsive to .actuation of the keying means for gradually reducing the applied potential.

Another feature of the invention is that the system includes a source of potential with tworditierent potential levels, switch means for selecting the nature of operation of the musical instrument and having iirst ,and second positions, a circuit completed in the first position of the switch means connecting the lamp with the source at one level of potential, a circuit-completed in the second position of the switch means connecting the lamp with the source at the other level of potential, keying means for completing the selected one of the circuits and means in the second circuit responsiverto actuation of the keying means for graduallyv reducing the applied potential. Preferably, the potentialrapplied to the lamp in the second position of the selector switch is higher than the potential appliedto the lamp in the first position thereof. This enhances the percussive eiect by accentuating the leading edge or initial portion of a percussed tone;

Yet a further feature is the provision of a percussion system including .a source of potential, keying means connecting the tone generating system in a circuit with the source of potential and a variable impedance switch, as a saturable transistor amplifier, in the circuit. Yet a further feature in the incorporation in the system of a capacitor having a charge path completed from the potential source through the variable impedance switch, the potential on the capacitor controlling the impedance of the switch providing gradual decay of the generated tone.

Further features and advantages of the invention will readily be apparent from the following specification and from the drawings, in which:

FIGURE l is a fragmentary diagrammatic illustration of the basic photoelectric tone generating'system with which the percussive keying system of the present invention is particularly useful; i f r FIGURE 2 is a block diagram of a keying sy'stem for the lamps of a photoelectric cell tone generator; and

FIGURE 3 is a schematic circuit diagram of a percnssion keying system embodying the invention.

In an electronic musical instrument utilizing vacuum tube oscillators, percussive effects may be obtained by varying an operating condition of each oscillator. The system described and claimed herein is concerned with the production of percussive eifects by controlling the potential applied to the lamps of the photoclectric cell tone generators.

Turning now to the drawings, FIGURE 1 illustrates diagrammatically the basic elements of the tone generating system, including a lamp 10, a mask plate 11 having a light transmitting opening 11a, a scanning disc i2 having a plurality of scanning slots 12a and a photoelectric cell i3. Scanning disc 12, as its name implies, moves relative to the mask 11 and as slots 12a move past opening lla, light from lamp 10 is transmitted through the slots to the photoelectric cell. The amplitude of the transmitted light varies in accordance with the configuration of mask area 11a as the slot moves across the mask. This light variation produces a corresponding Variation in the electrical current flowing through photoelectric cell 13 generating a tone representing signal. The electrical signal may in turn be ampliiied and reproduced through a loud-speaker system. The complete electronic organ may include a plurality of mask and scanning disc assemblies, each of which has a plurality of mask openings and associated lamps, depending upon the characteristics of the particular instrument.

FIGURE 2 illustrates the basic keying system for such an instrument in which the lamps 10 are connected from one -terminal of a source of potential 1S through a stop lselector mechanism 16 to a plurality of key switches I7 which are returned through a common reference potential or ground 1S to the potential source. When each of the keys 17 is actuated, circuits are completed energizing one or more lamps l() as required lto produce the desired tones depending upon the number of stop selectors '16 and the number of keys depressed. With the system thus far described, the lamps 1) are energized at the relatively constant potential of source I5. Connected in series with the ground return from key switches 17 is a percussion selector switch 19 shown in its first position which, when moved to the On position or second position connects a percussion generator 2li in series with the keying circuit. The function of the percussion generator, as will appear in more detail below, is lto provide an energization potential for the lamps 10 which has a quick rising or steep leading edge upon actuation of the key switch and preferably of an amplitude greater than that of source 15, followed by a gradual, preferably exponential, decline or decay. The exponential decay of the vol-tage or potential applied to the selected lamps upon actuation of lthe key switches causes a corresponding decay of the light output of the lamp and of the tone representing signal generated in photoelectric cell 13. The rate of decay of the applied potential is preferably variable to permit the simulation of different types of percussive instruments.

Turning now to FIGURE 3 a specific embodiment of a percussion keying system is illustrated. Considering first the operation of the circuit with switch 19 in the percussion Off position, it will be seen that when key switch 17 is closed a circuit is completed from power source 15 through lamp itl and the ground or common return 118 energizing the lamp. Power source 15 may have a voltage of the order of 10 volts and this full voltage is applied to lamp 1G so long as key switch 17 remains in the actuated or closed position. n

To provide a percussive effect, it is desirable that the potential initially applied to the lamp not only have a aoc/anos steep leading edge or fast rise time, but that it be higher in amplitude than the potential applied in the non-percussive condition c-f the system. This serves two purposes: one, it aids in bringing the lamp rapidly to an incandescent condition; and two, as the peak amplitude of the percussed note is relatively short in duration, the somewhat higher amplitude than a sustained note, provides an effect perceived by a listener that the percussed note is of equal amplitude or intensity.

Briefly, the percussion generator circuit includes a second source Z2. or potential which is connected through percussion switch 19 and a circuit Z3, sometimes referred to herein as a variable impedance switc in series additive relation with potential source l5 for energizing lamp 10. With percussion switch 19 in the On position, when key switch 17 is actuated the sum of the potentials from sources 15 and 22 is applied to lamp lil. Circuit 23 'clocks within a fraction of a second, acting as a short circuit. in the meantime, however, capacitor 24 charges from the two sources and following saturation of circuit 23 controls the impedance of the switch as it discharges providing the desired exponential decay.

rthe circuit will now be described in more detail and during the course of the description, values and type designations will be assigned to the various circuit elements. It is to be understood that this detailed disclosure is intended solely as an example of an operative embodiment of the invention and many changes and modilications will readily be apparent to those skilled in the art.

Potential source 22 includes a step-down transformer 3i) with a full wave rectifier circuit including a pair of diodes 31, type lN 1450, which charge capacitor 32, 6,000 af., with the polarity indicated. rlhe positive terminal of capacitor 32 is grounded to connect the two potential sources in series additive relation. The no load output voltage of secondary potential source Z2. is ofthe order of four volts.

Blocking switch 23 includes transistors 33, 2N441, 34, ZNZt, and 35, 2N270, connected in a cascade high gain amplifier circuit. The emitter-collector circuit of transistor 33 is connected in series in the circuit of lamp d0, across series connected power sources l5 and 22. The input of transistor 35 is coupled to secondary winding Sb of pulse transformer 36, the primary winding 36a of which is serially connected in the lamp circuit. When key switch 17 is closed, a relatively small current flows through the lamp circuit, limited by the impedance of transistor 33 and the number of lamps being lit. The small current produces a voltage in the secondary winding which is applied to the transistor hy the transistors to substantially lower the impedance of transistor 33 and thereby increase the current in the keying circuit. This increased current is reamplilied and again coupled back to the lamp circuit. This re-arnplification of the signal through the amplifier circuit vtakes place extremely rapidly and re-amplication may occur many times in a fraction of a second unti the current through transistor 33 saturates it. With transistor 33 saturated variable impedance switch circuit 23 appears as a short circuit connecting lamp across sources and Z2 in additive relation. The rapid decrease in impedance provides a rapid, high level of initial energization of lamp 10, and may reach the order of l2 volts. The output of secondary potential source 22 drops to about 2 volts when current is drawn therefrom.

Resistor 37, 220 ohms, is shunted across the secondary Winding of pulse transformer 36 and dampens the feedback pulse slightly. This prevents excessive buildup of the current through the circuit with a large load, as when several keys are depressed simultaneously, and undesired triggering of the percussion circuit with other changes in the organ system as when a key is opened in the lower manual, for example, causing a slight voltage increase in the potential source 15.

35 and amplilied During conduction of the transistors, capacitor 24, 250 at., is connected through the emitter-collector circuit of transistor 35 across the series combination of potential sources 15 and 22 and charges to a potential of the order of 10 to 12 volts. When the transistor amplifier saturates, capacitor 24 the potential across which y is applied to the emitter of transistor 35, controls the impedance of switch circuit 23. Connected across capacitor 24 is a circuit including resistor 38, 1,000 ohms, variable resistor 39, 10,000 ohms, and resistor `40, ohms through which the capacitor discharges. As the potential across capacitor 24 decreases, the impedance of switch 23 ini creases decreasing the potential applied to lamp 10. Resistor 39 may be utilized to vary the shunt impedance connected across capacitor 24 and thus to vary the time of discharge of the capacitor and the decay time of the generated tone. Resistor 38 limits the decay time by providing a minimum resistance in the circuit.

The voltage divider of which resistor 40 is a part includes resistor 41, 680 ohms, with the two resistors connected in series across ten volt supply 15. The potential across resistor 40 is of the order of the 1.5 to 2.0 volts. This voltage keeps a small residual charge on capacitor 24 which maintains a low level of conduction through the transistors insuring rapid build-up of amplification with a smallload, as when only one lamp 10 is in the circuit.

While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of many modifications. Changes therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

1. In an electronic musical instrument utilizing a tone generator incorporating a lamp, the generated tone having an amplitude which is a function of the potential applied to the lamp, a keying system including: means providing a source of potential with two levels of potential; switch means for selecting the nature of operation of said musical instrument and having a first and a second position; a circuit completed in the first position of said switch means connecting said lamp with said source at one level of potential; a second circuit completed in the second position of said switch means connecting said lamp with said source at the other level of potential; keying means for completing the selected one of said circuits, applying a potential to said lamp; and means in said second circuit, responsive to actuation of said keying means for gradually reducing the applied potential.

2. The keying circuit of claim `l, wherein the potential applied to the lamp with the selector switch means in the second position is higher than the potential applied to the lamp with said switch means in the rst position.

3. In an electronic musical instrument utilizing a tone generator incorporating a lamp, the generated tone having an amplitude which is a function of the potential applied to the lamp, a keying system including: means providing a source of potential with two levels of potential; switch means for selecting the nature of operation of said musical instrument and having a rst and a second position; a circuit completed in the rst position of said switch means connecting said lamp with said source of potential at one level; a second circuit completed in the second position of said switch means connecting said lamp with said source of potential at a higher level; keying means for completing the selected one of said circuits, applying a potential to said lamp; means in said second circuit, responsive to actuation of said keying means for gradually reducing the applied potential at an exponential decay rate with time; and means in said second circuit for varying the rate of decay.

4. In an electronic musical instrument utilizing a tone generator incorporating a lamp, the generated tone having an amplitude which is a function of the potential applied to the lamp, a keying system including: means promusical instrument and having a first and a second posi# tion; a circuit completed in the first position of said switch means connecting said lamp with said source at one level of potential; a second circuit completed in the Y second position of said switch means connecting said lamp with said source at the other level of potential; keying means for completing the selected one of said circuits, applyiing a potential to said lamp; a transistor amplifier in said second circuit including means for overdriving and Asaturating said transistor amplifier; and means for gradually increasing the impedance of said a'mpliiier.

5. In an electronic musical instrument utilizing a tone generator incorporating a lamp, the generated tone having an amplitude which is -afunction of the potential applied to the lamp; a keying system including: a first source of potential; a second source of potential; switch means for selecting the nature of operation of said musical instrument and having a first and a second position;

a circuit completed in the iirst position of said switch means connecting said lamp with said first source of potential; a second circuit completed in the second position of said switch means connecting said lamp with both of -said sources of potential in additive relation; keying means for completing the selected one of said circuits, applying the selected potential to said lamp; a transistor amplifier in said second circuit including means for overdriving and saturating the transistor amplifier; and means for gradually increasing the impedance of said ampliiier.

6. In an electronic musical instrument utilizing a tone generator incorporating a lamp, the generated tone having a characteristic related to the potential applied to said lamp, a percussion keying system including: a first source of potential, a second source of potential; switch means for selecting the nature of operation of said musical instrument and having a iirst and a second position; a key switch; a iirst circuit completed in the first position of said switch means, through said key switch, connecting said lamp with the first of said sources of potential; a second circuit completed in the second position of said switch means through said key switch connecting said lamp with both of said sources of potential in series additive relation; a transistor amplierin said second circuit including means for over-driving and saturating said transistor, and

forming a variable impedance switch; a capacitor having a charge path completed from said source through said variable impedance switch and controlling the impedance of said switch; and a discharge path for said capacitor.

7. In an electrical musical instrument of the type in which a tone generator including a lamp generates a tone signal the amplitude of which is a function of the potential applied to the lamp and in which a circuit including a keying means energizes the lamp, in combination with the lamp energizing circuit a percussion circuit comprising a transistor connected in the lamp energizing circuit, bias means providing a transistor impedance which permits 'initial conduction therethrough at a low current value incident to actuation of the keying means, and means coupled to the energizing circuit and to the transistor responsive to the initial current liow rapidly decreasing the transistor impedance and subsequently increasing the impedance at a desired rate while the keying means is actuated.

8..In an electrical musical instrument of the type in which a tone generator including a lamp generates a tone signal the amplitude of which is a function of the potential applied to the lamp and in which a circuit including a keying means energizes the lamp, in combination with the lamp energizing circuit a. percussion circuit comprising an amplifier connected in the lamp energizing circuit, bias means providing an amplifier impedance which permits initial conduction therethrough at a low current value incident to actuation of the keying means, and means coupled to the energizing circuit and to the amplifier responsive to the initial current flow rapidly decreasing the amplifier impedance and subsequently increasing the impedance at a desired rate while the keying means is actuated.

9. In an electrical musical instrument of the type in which a tone generat-or including a lamp generates a tone signal the amplitude of which is a function of the potential applied to the lamp, and in which a circuit including a keying means energizes the lamp, in combination with the lamp energizing circuit a percussion circuit comprising a transistor connected in the lamp energizing circuit, bias means providing a ltransistor impedance which permits initial conduction therethrough at a low current value incident to actuation of the keying means; and means, including a pulse transformer coupled to the energizing circuit and at least one transistor amplifier having an input connected to the transformer and an output coupled to the first-mentioned transistor, responsive to the initial current flow rapidly decreasing the impedance of the iirstmentioned transistor and subsequently increasing the im pedance at a desired rate while the keying means is actuated.

10. The combination claimed in claim 9 in which the last-mentioned means includes a capacitor coupled to the amplifier and charged by the ampliiier while the impedance of the first-mentioned transistor is decreased, and a resistor discharge pat-h for the capacitor to decrease the charge across the capacitor for decreasing the amplifier gain and the impedance of the yiirst-mentioned transistor at the said desired rate.

References Cited in the file of this patent UNITED STATES PATENTS 2,924,784 Peterson Feb. 9, 1960' 2,946,252 Clark July 25, 1960 3,003,383 Williams Oct. 10, 1961 

1. IN AN ELECTRONIC MUSICAL INSTRUMENT UTILIZING A TONE GENERATOR INCORPORATING A LAMP, THE GENERATED TONE HAVING AN AMPLITUDE WHICH IS A FUNCTION OF THE POTENTIAL APPLIED TO THE LAMP, A KEYING SYSTEM INCLUDING: MEANS PROVIDING A SOURCE OF POTENTIAL WITH TWO LEVELS OF POTENTIAL; SWITCH MEANS FOR SELECTING THE NATURE OF OPERATION OF SAID MUSICAL INSTRUMENT AND HAVING A FIRST AND A SECOND POSITION; A CIRCUIT COMPLETED IN THE FIRST POSITION OF SAID SWITCH MEANS CONNECTING SAID LAMP WITH SAID SOURCE AT ONE LEVEL OF POTENTIAL; A SECOND CIRCUIT COMPLETED IN THE SECOND POSITION OF SAID SWITCH MEANS CONNECTING SAID LAMP WITH SAID SOURCE AT THE OTHER LEVEL OF POTENTIAL; KEYING MEANS FOR COMPLETING THE SELECTED ONE OF SAID CIRCUITS, APPLYING A POTENTIAL TO SAID LAMP; AND MEANS IN SAID SECOND CIRCUIT, RESPONSIVE TO ACTUATION OF SAID KEYING MEANS FOR GRADUALLY REDUCING THE APPLIED POTENTIAL. 